public class problem2 {
    int m, n;
    int[] dx = {0,0,1,-1};
    int[] dy = {1,-1,0,0};
    boolean[][] vis;
    char[] word;

    public boolean exist (String[] board, String _word) {
        // write code here
        m = board.length;
        n = board[0].length();
        vis = new boolean[m][n];
        word = _word.toCharArray();

        for(int i = 0; i < m; i++) {
            for(int j = 0; j < n; j++) {
                if(board[i].charAt(j) == word[0]) {
                    if(dfs(board,i,j,0) == true) {
                        return true;
                    }
                }
            }
        }
        return false;
    }

    public  boolean dfs(String[] board, int i, int j, int pos) {
        //结束条件
        if(pos == word.length-1) {
            return true;
        }

        vis[i][j] = true;
        for(int k = 0; k < 4; k++) {
            int x = i + dx[k];
            int y = j + dy[k];
            if(x >= 0 && x < m && y >= 0 && y < n && !vis[x][y] && board[x].charAt(y) == word[pos+1]) {
                if(dfs(board, x, y, pos+1)) {
                    return true;
                }
            }
        }
        vis[i][j] = false;

        return false;
    }
}
